Abstract:
Molecular diversity is critical for improvement of Economic Traits (ET) in Indigenous Turkeys (IT). Poor productive performance constitutes one of the main constraints to improvement of ET of IT which can be ameliorated by application of knowledge of variation in growth-influencing genes. Information on the variability in genes influencing growth traits of IT in Nigeria are inadequate. Therefore, diversity in selected growth-influencing genes in associations with growth traits of IT in Southwestern Nigeria were investigated.
Three hundred mature IT (124 Toms and 176 Hens) comprising 82 black, 114 spotted and 104 white strains were randomly sampled across southwestern states. Blood (2 mL) was collected from the IT to detect polymorphisms at Insulin-like Growth Factors 1 and 2 (IGF1, 1GF2), Growth Hormone (GH), GH Receptor (GHR) and myostatin genes using standard procedures. Poults hatched (n=300) from randomly purchased IT eggs were sorted (70 black, 140 spotted and 90 white strains) and managed for 21 weeks. Weekly Bodyweight (WB) was monitored for association of polymorphic variants and growth using standard method. At week 10, blood (2 mL) was sampled from each strain (n=60). The DNA was extracted, amplified, electrophoresed, sequenced and genotyped with restriction fragment length polymorphism. The WB and carcass traits at week 21 were associated with each of IGF1, 1GF2, GH, and myostatin genes. Allele and genotype frequencies, F-statistics, and test of Hardy-Weinberg’s Equilibrum (HWE) were computed and phylogenetic tree constructed across genotypes. Parameter estimates were obtained from four non-linear growth models (Brody, Gompertz, Logistic and Von-Bertalanffy) that differ in goodness of fit, biological interpretation and ease of computation. The WB and carcass traits data were analysed using ANOVA at ᾳ0.05
Co-dominant alleles A and B corresponding to genotypes AA, AB and BB were detected across each of the five loci tested. Allele frequencies were between 0.73 (A) and 0.26 (B). Heterozygosity excess (Fst) ranged from -0.007 (IGF1) to -0.003 (myostatin) within strains. The closest genetic distance (0.001) was between spotted and white strains while farthest (0.005) was between black and white strains. Spotted (GHR and myostatin), white (GH and myostatin) and black (IGF1, IGF2 and GH) strains conformed with HWE. Bodyweight at week 21 had significant association with BB genotype for black (2731.2±44.7), spotted (2118.3±289.6) and white (2280.6±94.3) at myostatin locus. Genotype BB in IGF1 and GH loci were superior to AA and AB genotypes in breast weight for black and white strains. Genotype BB of toms and hens had significant association with wing weight at IGF1 (241.1±12.3 and 190.7±8.7) and myostatin (233.6±14.1 and 190.2±12.1, respectively). Logistic and Brody models fitted best in black (AA), spotted (BB) and white (AB) at IGF1 locus. At IGF2 and GH loci, Von-Bertalanffy was the best on AB genotype across the strains while Gompertz fitted best in black (BB), spotted (AA) and white (BB) at myostatin locus.
Growth-influencing genes examined were polymorphic. Genotype BB was superior in growth at Insulin-like growth factors 1 and 2, growth hormone and myostatin loci and could be explored in marker-assisted selection for genetic improvement.
